Propylene oxide is used in the production of polyether polyols, which are precursors in the manufacture of polyurethane resins, and in the production of propylene glycol.
The traditional route for the production of propylene oxide proceeds via the conversion of propylene to chloropropanols, which then undergo dehydrochlorination to the desired oxide. More recently, interest has focused on oxidation methods, for example the direct oxidation of propylene with hydrogen peroxide or the co-oxidation of propylene with isobutene, ethylbenzene, or cumene.
U.S. Pat. No. 6,984,761 discloses a process for co-producing propylene oxide and α-methyl styrene along with phenol and acetone by oxidizing cumene to cumene hydroperoxide and then reacting part of the cumene hydroperoxide with propylene in the presence of an epoxidation catalyst to form propylene oxide and dimethyl phenyl carbinol. The propylene oxide is separated from the reaction stream leaving a stream containing dimethyl phenyl carbinol. The dimethyl phenyl carbinol-containing stream and the remaining portion of the cumene hydroperoxide stream are converted in the presence of a catalyst, preferably an acidic catalyst, to form a product stream containing phenol, acetone, and α-methyl styrene.
The process of '761 patent allegedly has the advantage that, by controlling the fraction of the cumene hydroperoxide converted to dimethyl phenyl carbinol, the amount of α-methyl styrene produced can be continuously set to meet the market demand for α-methyl styrene. However, the world demand for α-methyl styrene is limited. Moreover, the market for phenol is growing more rapidly than that for the acetone co-product.
According to the invention, it has now been found that propylene oxide can be produced by reaction of propylene with cyclohexylbenzene hydroperoxide in the presence of an epoxidation catalyst. This process has the advantage that its co-product is phenylcyclohexanol, which can readily be converted to cyclohexylbenzene by dehydration to phenylcyclohexene followed by hydrogenation of the phenylcyclohexene. The cyclohexylbenzene can then be recycled back to the oxidation step used to produce the cyclohexylbenzene hydroperoxide. Moreover, by supplying part of the cyclohexylbenzene hydroperoxide to a cleavage reaction, it is possible to co-produce phenol/cyclohexanone with the propylene oxide. Not only is cyclohexanone of more value than the α-methyl styrene co-product of the '761 patent but, if desired, part or all of the cyclohexanone can be dehydrogenated to produce additional phenol. Moreover, the ratio of propylene oxide to phenol/cyclohexanone can be readily adjusted according to their relative market demands.